The invention relates to a sensor arrangement for a motor vehicle for detecting an environment having at least two camera systems.
A sensor system of this type can be used, for example, for assisting the driver, thus for supporting an operator of a vehicle. It supplies information on the environment and can be used in the domain of lane tracking, for a warning in the case of a lane deviation, or in the domain of automatic vehicle guidance.
In the case of such sensor systems, it is known to use so-called CCD cameras (CCD=charged coupled device). However, it should be taken into account that the functionality of driving assistance systems is limited when the sensor is already subjected to limitations when detecting the environment. In the case of CCD cameras, it is known that, especially in darkness and in the event of blinding due to an external light source, these cameras have a limited functionality. In this case, with respect to a blinding light in darkness, a superproportional limitation should be taken into account, specifically when the CCD camera is adjusted to the environmentally caused illumination level. In the event another vehicle driving with switched-on lights is encountered, the image information is even largely destroyed by the oncoming blinding light sources.
The use of infrared cameras in such sensor arrangements is also known (see. e.g. technical journal: CAR AND DRIVER, October 1998). Infrared cameras obtain a heat image of the driving environment. In the heat image, all contours and objects are based on thermal contrasts. However, the information which is important for the driving task or for the reaction of a driver assistance system cannot always be obtained from the heat image.
European patent document EP 0 454 516 A1 describes an obstacle detection system having two video cameras, which generate images in the visible and in the infrared range. For generating images in the infrared range, CCD technology is used, for example. By means of a similar video camera, which can detect the entire spectrum, a differential signal is generated. This differential signal or differential image relates to the visual range, which is covered by the cameras and is based on the contrast of an object in this visual range. Japanese patent document JP-10 255019 also describes a system with a CCD camera, which generates a visible image from the area in front of a vehicle. Furthermore, an infrared image is generated by an additional infrared camera. Based on the temperature information, a threshold for illuminated parts is generated, and an improved vehicle detection can take place on the basis of this threshold.
It is an object of the present invention to further develop a sensor arrangement of the above-mentioned type such that the environment can be detected essentially without any limitation of the functionality.
This object is achieved by a sensor arrangement for a motor vehicle for detecting the environment using at least two camera systems. Each camera system operates in a different spectral region. Each camera system is adjusted to obtain images in different distance ranges.
An essential idea of the invention is to use at least two camera systems with respectively different spectral operating regions.
In this case, the different camera systems are adjusted to different distance ranges. For example, an infrared camera takes over the environmental detection in the remote range because it is suitable for day and night use and is free from the effects of blinding. Freedom from blinding means, in this context, that the individual pixels are not overmodulated by the headlights of oncoming vehicles. The image information is therefore retained although the environment is completely dark. The close range is detected by the CCD camera. In particular, the CCD camera is adjusted such that it operates in a range which is illuminated by the front headlights when the vehicle headlights are switched on. Because of the higher illumination level, this measure reduces the susceptibility of the CCD camera to blinding effects.
According to a preferred embodiment, the sensor arrangement comprises a CCD-camera (charged coupled device) and a camera which operates in the infrared range. The infrared camera represents, for example, a meaningful supplementation of the sensor system (CCD), which is visual here, beyond its detection limits in the extended area in front of the driving environment.
When using camera systems adjusted to different distance ranges and with connected imaging scales, the driving environment, as a whole, can be detected better in both the close and remote ranges.
Another advantage of using two camera systems with different spectral operating regions consists of determining the atmospheric absorbance in the two spectral regions via differential contrast evaluation, a comparison of differences in contrast between objects and their environments. Because atmospheric absorbances have different effects on images formed by different camera systems adjusted to different distance ranges, by comparing differences in contrast observed by the different camera systems (which are indicative of the atmospheric absorbances), conclusions can be drawn with respect to the extent of fog or haze. Furthermore, in conjunction with a visual range model stored in a vehicle, a driver's visual range can be determined from the detected absorbances. This information, in turn, can be made available to the driver, or control parameters can be adjusted in the vehicle as a function of the determined driver's visual range.
These and other advantageous embodiments are defined in the subclaims.